Preparation of unsaturated hydrocarbons by pyrolysis, and related compositions



' pane, and butane, and of natural United States Patent ()fifice3,366,702 PREPARATION OF UNSATURATED HYDRO- CARBONS BY PYROLYSIS, ANDRELATED COMPOSITIONS Francis C. Moriarty, Findlay, Ohio, assignor toMarathon Oil Company, Findlay, Ohio, a corporation of Ohio No Drawing.Filed May 3, 1965, Ser. No. 452,842 Claims. (Cl. 260-679) ABSTRACT OFTHE DISCLOSURE The present invention comprises, in the preparation ofunsaturated hydrocarbons by the pyrolysis of hydrocarbons by passingthem through a heated furnace and thereafter separating out the productsthus produced, the step comprising injecting an effective amount of anoxy-compound inhibitor into the process stream at a point downstreamfrom said furnace to reduce the formation of solid deposits.

The invention further comprises gaseous hydrocarboncontainiugcompositions inhibited against varnish formation comprising 10 to about90 mole percent acetylene and derivatives, 10 to about 90 mole percentethylene and derivatives, and 0.0001 to 0.05 mole percent of anoxycompound inhibitor. Unsaturated hydrocarbons are useful as chemicalintermediates and particularly as starting materials for the formationof various polymers.

The present invention relates to the preparation of unsaturatedhydrocarbons and in its preferred embodiments relates to improvedprocesses for the preparation of acetylene and ethylene from non-gaseoushydrocarbons.

Processes for thermally cracking hydrocarbons into acetylene, ethylene,and other unsaturated gases have been described at length in theliterature. (See, for example, the Wultf Process described in US.Patents 1,996,185; 2,037,056; 2,236,534; 2,236,535; 2,236,555;2,319,679;

' of methane, ethane, progas to form acetylene and ethylene haveparticularly been studied. (See, for example, Tropsch and Englotf,Industrial and Engineering Chemistry, 27, page 1063 (1935), and US.Patent 1,983,- 992.) As illustrated by US. 2,236,534, FIGURE 1, suchprocesses typically consist of a furnace in which the thermal crackingof hydrocarbons is accomplished generally at temperatures above aboutl,500 F. for carefully controlled contact periods generally less thanabout lO seconds. A rapid cooling of the efiluent from the furnace isusually essential to the attaining of the desired ethylene and acetyleneproducts. By control of the process conditions, the percentage ofacetylene and ethylene can be controlled generally within the range ofabout 10 to 90 mole percent of each.

The hydrocarbons fed to such processes have generally been the gaseousaliphatic hydrocarbons, i.e., methane, ethane, propane, and butane. Inutilizing such feed ma terials the furnace produces a substantial amountof tars which are removed by a trap located in the efiluent stream. Evenwith an efiicient trap, some build-up of tars is encountered in theequipment downstream from the trap. Since the separation of the efiluentacetylene and ethylene requires a relatively complex selectiveabsorption and stripping section, maintenance in removing tar depositsfrom this equipment can present a significant problem.

Current markets for petroleum products have made it economicallyexpedient to utilize the Wullf process with much higher boiling feedstocks than the gaseous hydrocarbons commonly employed. These feedstocks, primarily heavy naphthas having boiling ranges of approximately200 to 400 F., form substantially greater amounts of 3,366,762 PatentedJan. 30, 1968 deposits. Further, these deposits, while originally softand tacky, solidify with time into relatively hard material which isdiflicult to remove from the interior of equipment.

The present invention embodies the discovery that these deposits areprimarily composed of oxygenated varnishlike materials which areapparently primarily formed from diolefins, especially diacetylenes.According to the invention, by the addition of certain inhibitors intothe process stream at a point downstream from the furnace, formation ofvarnishes is reduced and those varnishes which form are maintained in asubstantially fluid condition. By maintaining the varnishes in a fluidcondition, they are prevented from depositing on equipment and arereadily removed with other fluid by-products of the process.

While the process of the present invention may be practiced Withoutconventional tar removal, in order to minimize the amount of inhibitorsrequired, a conventional tar placed upstream from the point of injectionof the inhibitors. Most preferably, the inhibitors are injecteddownstream from the tar removal apparatus at a number of points sospaced as to maintain a relatively constant concentration of theinhibitor in each of the process streams in which tar formation islikely to occur.

The inhibitors to be utilized with the present invention are notnarrowly critical. In general, inhibitors which prevent the formation ofoxy substances, and particularly those which prevent the formation ofperoxides have been discovered to be valuable. While the presentinvention is not to be taken as being dependent upon any mechanism bywhich the formation of deposits or the inhibition occurs, it is believedthat the formation of peroxides greatly accelerates the formation ofdeposits and the solidification of such deposits.

Thus, while tertiary butyl catechol is the most preferred inhibitor forthe process of the present invention, other oxy-compound inhibitorsincluding other alkyl catechols, cresylic acid and its derivatives,butyl phenols, phenylene diamine, 2,4,6-trimethylphenol,2,4-dimethyl-6-t-butylphenol, 2,4-dimethyl-6-isobutylphenol,2,6-di-sec-butyl-4- methylphenol, 2,6-di-t-butyl-4-isopropylphenol,N,N'-di- (sec-butyl)-p-phenylene diamine, p-phenylene diamine,N,N'-di(tert-butyl)-p-phenylene diamine, and p-butylaminophenol areuseful in the process. All such inhibitors are included within the termoxy-compound inhibitor as used herein.

The inhibitors will be utilized in whatever mole percent is found togive 'best results at reasonable cost. Generally from about 0.0001 toabout 0.05 mole percent inhibitor will be injected based on the moles ofproduct. The molecular weights of inhibitors may be chosen so as toprovide desirable boiling points and other physical properties, e.g., byvarying the length of the alkyl group in alkyl catechols. A mixture ofdifferent inhibitors may be desirable under some circumstances. Whileheavier feeds normally produce larger amounts of viscous deposits, itshould be understood that the present invention is beneficial when crudeoils, light and heavy naphthas, gaseous hydrocarbons and other feedstocks are utilized in the Wulif Process and analogous processes.

The preceding discussions and the following examples are intended to bemerely illustrative of the invention and the claims are to be taken asincluding all of the variations and modifications which would beapparent to one skilled in the art.

Example I A naphtha feed stock having a boiling range of from about 250to 350 F. is fed to a modified WuliT process according to the process ofUS. 2,236,534. The maximum temperature in the furnace is approximately2,400 F. and the residence time is approximately 0.015 second. The

effluent from the furnace is quenched and immediately upon leaving thequencher, the product stream is injected with 0.01 mole percenttert-butyl catechol. Gummy varnishes, which solidify forming harddeposits on the downstream :separatory equipment, are not encountered,although such deposits are encountered when the injection of thetert-butyl catechol is discontinued.

What is claimed is:

1. In the process for the preparation of unsaturated hydrocarbons by thepyrolysis of hydrocarbons by passing them through a heated furnace andthereafter separating out the products thus produced, the stepcomprising injecting an effective amount of an oXy-compound inhibitorinto the process stream at a point downstream from said furnace toreduce the formation of solid deposits.

2. In a Wulif-type process involving the pyrolysis of hydrocarbons atshort residence times in a furnace followed by a rapid cooling of theeffluent from the furnace, the step comprising injecting into theprocess stream after said rapid cooling from 0.0001 to about 0.05 moleof an oxy-compound inhibitor per mole of product to reduce the formationof solid deposits.

3. The process of claim 1 wherein the oXy-compound inhibitor is an alkylcatechol.

4. The process of claim 1 wherein the oXy-compound inhibitor is selectedfrom the group consisting of cresylic acid and cresylic acidderivatives.

5. The process of claim 2 wherein the oxy-compound inhibitor is an alkylcatechol.

6. The process of claim 2 wherein the oxy-compound inhibitor is selectedfrom the group consisting of cresylic acid and its derivatives.

7. Gaseous hydrocarbon-containing compositions inhibited against varnishformation comprising 10 to about mole percent acetylene and derivatives,10 to about 90 mole percent ethylene and derivatives, varnish-formingmaterials and 0.0001 to 0.05 mole percent of an oXy-cornpound inhibitor.

8. The process of claim 7 wherein the oxy-cornpound inhibitor is analkyl catechol.

9. The process of claim 7 wherein the oXy-compound inhibitor is selectedfrom the gr'oup'consisting of cresylic acid and its derivatives.

10. The compositions of claim 7 wherein the oxy-compound inhibitor istert-butyl catechol.

References Cited UNITED STATES PATENTS 2,038,630 5/1936 Bennett et al4478 FOREIGN PATENTS 599,733 4/ 1948 Great Britain.

DELBERT E. GANTZ, Primary Examiner. J. D. MYERS, Assistant Examiner.

